1. Field of the Invention
This invention relates to a butterfly valve comprising a valve housing having bearing portions, a valve stem rotatably supported by the bearing portions, tubular bearing members slidably and fixably disposed between the bearing portions and the valve stem, a valve body mounted on the valve stem, a plurality of valve seats attached to the valve housing to contact the periphery of the valve body in a closed position, and elastic seal members to contact the bearing portions over the entire inner peripheral surfaces thereof, entire outer peripheral surfaces of annular recesses defined between the valve body and the valve stem, and, at both sides of the valve stem, the inner peripheral surfaces of the bearing portions, end surfaces of the valve seats, and the outer peripheral surfaces of the annular recesses, respectively, when the valve is closed.
2. Description of the Prior Art
A good leakproof condition may be maintained around the valve stem by having the elastic seal members contact the three elements, i.e. the inner peripheral surfaces of the bearing portions, the end surfaces of the valve seats, and the outer peripheral surfaces of the annular recesses.
In the prior art, each of the elastic seal members is pressed into a closed space defined between the above three surfaces and the valve stem. That is to say, the seal member is placed in direct contact with each of these elements that make relative rotations when the valve is opened or closed. Therefore, the valve stem is subjected to a great frictional resistance owing to the elasticity of the seal members at the time of opening and closing the valve, requiring a great driving force in operating the valve.